The patent application entitled ROTATING SEAL FOR GAS TURBINE ENGINE filed by Gary Paul Peters on even date, supra discloses an invention that constitutes an improvement over the lenticular seal disclosed and claimed in U.S. Pat. No. 3,733,146 granted to S. L. Smith & P. E. Voyer on May 15, 1973 and assigned to the same assignee as this patent application. This patent discloses a toroidally shaped seal disposed between the lst and 2nd turbine and is lenticular in cross section. Essentially, the inner and outer curved plates form an elliptical body that has its narrow ends abut against the adjacent disks of the turbines or the side plates thereof. This, in fact, forms a point attachment in cross section, and a circumferential edge attachment in full, being supported radially by the turbine disks and transmitting the axial load through both curved plates. In operation, the plates achieved their results, that is, net reduced stress, by virtue of the bending of the plates. Obviously, the higher the bending loads the heavier the plates have to be so as to tolerate the higher bending stresses. The seal disclosed in the patent application, supra, is an "I" Beam shaped, in cross section seal, where the outer rim spans between adjacent stages of turbines and engage the disks in a judicial manner.
In the type of turbine/seal construction disclosed in the U.S. Pat. No. 3,733,146 supra, it is typical to include cover plates on the front face of the lst and 2nd stage turbines adjacent the juncture where the root of the blade fits into the broached recess in the turbine disk. The cover-seals (sometimes referred to as mail boxes because of the likeness in shape) are a plurality of flat elements (one for each blade) that are spaced around the circumference of the disk. An extension from the rear of the flat element extends into the broached fir tree recess at the juncture where the root of the turbine blade fits into this recess. In the prior art designs the sole purpose of the cover plate was to define an aerodynamically smooth contour on the face of the disk to avoid pressure penalty. Thus it was merely a windage cover.
I have found that I can utilize these cover-seals not only as a windage cover but also to attain a cooling of the disk. According to the invention the axial extension of the cover extending into the broach area radially outside the disk rim and radially supported by the blade, is judiciously spaced radially from the rim to provide a dead ended annular space. The cooler air in the root cavity migrates to this space and insulates the disk rim from the engine's extremely hot working medium that is acting on the turbine blades. Tests have shown that this feature reduces the disk rim temperature by over 100.degree. F. which (1) increases the disk low cycle fatigue life and (2) allows the use of less expensive material from which the disk is fabricated.